 
Summary: David Kerr
Texas A&M
University
Friday
Nov. 12, 2010
3:30 p.m.
CL 408
The concept of entropy was introduced into ergodic theory by
Kolmogorov in the late 1950s. It can be viewed as a measure of the
average information gained in learning that the orbit of an unidentified
point visits a certain sequence of sets in a given partition of the space.
This dynamical version of Shannon's informationtheoretic entropy
revolutionize the study of measurepreserving actions, which until then
had relied on invariants of a spectral, as opposed to combinatorial,
nature. Entropy theory as originally conceived by Kolmogorov was
ultimately seen to apply most generally to actions of amenable groups,
for which one can average over partial orbits in a way that produces a
dynamical invariant.
Very recently Lewis Bowen showed, quite surprisingly, that the theory of
measure entropy can be vastly extended to the realm of actions of
